Semiconductor device with decoupling unit and method for fabricating the same

ABSTRACT

The present application discloses a semiconductor device and a method for fabricating the semiconductor device. The semiconductor device includes a first tier structure positioned on a substrate and including: a plurality of conductive features of the first tier structure positioned over the substrate, and a decoupling unit of the first tier structure positioned between the plurality of conductive features of the first tier structure, and including a bottle-shaped cross-sectional profile; a first set of solid alignment marks including: a first-tier-alignment mark of the first set of solid alignment marks positioned on the decoupling unit of the first tier structure; a first set of spaced alignment marks including: a first-tier-alignment mark of the first set of spaced alignment marks positioned in a mirror manner of the first-tier-alignment mark of the first set of solid alignment marks according to a first axis of symmetry.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device and a methodfor fabricating the semiconductor device, and more particularly, to asemiconductor device with a decoupling unit and a method for fabricatingthe semiconductor device with the decoupling unit.

DISCUSSION OF THE BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cellular telephones, digital cameras, andother electronic equipment. The dimensions of semiconductor devices arecontinuously being scaled down to meet the increasing demand ofcomputing ability. However, a variety of issues arise during thescaling-down process, and such issues are continuously increasing.Therefore, challenges remain in achieving improved quality, yield,performance, and reliability and reduced complexity.

This Discussion of the Background section is provided for backgroundinformation only. The statements in this Discussion of the Backgroundare not an admission that the subject matter disclosed in this sectionconstitutes prior art to the present disclosure, and no part of thisDiscussion of the Background section may be used as an admission thatany part of this application, including this Discussion of theBackground section, constitutes prior art to the present disclosure.

SUMMARY

One aspect of the present disclosure provides a semiconductor deviceincluding a first tier structure including a plurality of conductivefeatures of the first tier structure positioned over a substrate, and adecoupling unit of the first tier structure positioned between theplurality of conductive features of the first tier structure; a firstset of solid alignment marks including a first-tier-alignment markpositioned on the decoupling unit of the first tier structure, andincluding a fluorescence material; a second tier structure positioned onthe first tier structure and including a plurality of conductivefeatures of the second tier structure positioned over and deviated fromthe plurality of conductive features of the first tier structure, and adecoupling unit of the second tier structure positioned over the firsttier structure, and positioned between the plurality of conductivefeatures of the second tier structure; and a first set of spacedalignment marks including a second-tier-alignment mark positioned on thedecoupling unit of the second tier structure, and including afluorescence material. The decoupling units of the first tier structureand the second tier structure include a low-k dielectric material andrespectively include a bottle-shaped cross-sectional profile.

Another aspect of the present disclosure provides a semiconductor deviceincluding a first tier structure positioned on a substrate andincluding: a plurality of conductive features of the first tierstructure positioned over the substrate, and a decoupling unit of thefirst tier structure positioned between the plurality of conductivefeatures of the first tier structure, and including a bottle-shapedcross-sectional profile; a first set of solid alignment marks including:a first-tier-alignment mark of the first set of solid alignment markspositioned on the decoupling unit of the first tier structure; a firstset of spaced alignment marks including: a first-tier-alignment mark ofthe first set of spaced alignment marks positioned in a mirror manner ofthe first-tier-alignment mark of the first set of solid alignment marksaccording to a first axis of symmetry. The first-tier-alignment mark ofthe first set of solid alignment marks and the first-tier-alignment markof the first set of spaced alignment marks include a fluorescencematerial. The decoupling unit of the first tier structure includes alow-k dielectric material.

Another aspect of the present disclosure provides a method forfabricating a semiconductor device including forming a first tierstructure over a substrate and including: a plurality of conductivefeatures over the substrate, and a decoupling unit between the pluralityof conductive features; forming a first set of solid alignment marksincluding a first-tier-alignment mark on the decoupling unit of thefirst tier structure; forming a second tier structure over the firsttier structure and including: a plurality of conductive features overthe first tier structure, and a decoupling unit between the plurality ofconductive features; and forming a first set of spaced alignment marksincluding a second-tier-alignment mark on the decoupling unit of thesecond tier structure. The first-tier-alignment mark and thesecond-tier-alignment mark includes a fluorescence material. Thedecoupling units of the first tier structure and the second tierstructure include a low-k dielectric material.

Due to the design of the semiconductor device of the present disclosure,the first-tier-alignment marks, the second-tier-alignment marks, thethird-tier-alignment marks, and the fourth-tier-alignment marksincluding the fluorescence material may improve optical recognitionduring the wafer fabrication process. As a result, the yield offabricating the semiconductor device may be improved. In addition, thedecoupling units may reduce parasitic capacitance of the plurality ofconductive features.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and advantages of the disclosure will be describedhereinafter, and form the subject of the claims of the disclosure. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present disclosure. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the disclosure as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates, in a flowchart diagram form, a method forfabricating a semiconductor device in accordance with one embodiment ofthe present disclosure;

FIGS. 2 to 11 illustrate, in schematic cross-sectional view diagrams,part of a flow for fabricating the semiconductor device in accordancewith one embodiment of the present disclosure;

FIG. 12 illustrates, in a schematic top-view diagram, an intermediatesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 13 is a schematic cross-sectional view diagram taken along a lineA-A′ in FIG. 12 illustrating part of the flow for fabricating thesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 14 illustrates, in a schematic top-view diagram, an intermediatesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 15 is a schematic cross-sectional view diagram taken along a lineA-A′ in FIG. 14 illustrating part of the flow for fabricating thesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 16 illustrates, in a schematic top-view diagram, an intermediatesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 17 is a schematic cross-sectional view diagram taken along a lineA-A′ in FIG. 16 illustrating part of the flow for fabricating thesemiconductor device in accordance with one embodiment of the presentdisclosure;

FIG. 18 illustrates, in a schematic top-view diagram, a semiconductordevice in accordance with another embodiment of the present disclosure;

FIG. 19 is a schematic cross-sectional view diagram taken along linesA-A′ and B-B′ in FIG. 18 ;

FIG. 20 illustrates, in a schematic top-view diagram, a semiconductordevice in accordance with another embodiment of the present disclosure;

FIG. 21 is a schematic cross-sectional view diagram taken along linesA-A′ and B-B′ in FIG. 20 ;

FIG. 22 illustrates, in a schematic top-view diagram, a semiconductordevice in accordance with another embodiment of the present disclosure;

FIG. 23 is a schematic cross-sectional view diagram taken along linesA-A′ and B-B′ in FIG. 22 ;

FIG. 24 is a schematic cross-sectional view diagram taken along linesC-C′ and D-D′ in FIG. 22 .

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

It should be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected to or coupled to another element or layer, orintervening elements or layers may be present.

It should be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. Unless indicated otherwise, these terms areonly used to distinguish one element from another element. Thus, forexample, a first element, a first component or a first section discussedbelow could be termed a second element, a second component or a secondsection without departing from the teachings of the present disclosure.

Unless the context indicates otherwise, terms such as “same,” “equal,”“planar,” or “coplanar,” as used herein when referring to orientation,layout, location, shapes, sizes, amounts, or other measures do notnecessarily mean an exactly identical orientation, layout, location,shape, size, amount, or other measure, but are intended to encompassnearly identical orientation, layout, location, shapes, sizes, amounts,or other measures within acceptable variations that may occur, forexample, due to manufacturing processes. The term “substantially” may beused herein to reflect this meaning. For example, items described as“substantially the same,” “substantially equal,” or “substantiallyplanar,” may be exactly the same, equal, or planar, or may be the same,equal, or planar within acceptable variations that may occur, forexample, due to manufacturing processes.

In the present disclosure, a semiconductor device generally means adevice which can function by utilizing semiconductor characteristics,and an electro-optic device, a light-emitting display device, asemiconductor circuit, and an electronic device are all included in thecategory of the semiconductor device.

It should be noted that, in the description of the present disclosure,above (or up) corresponds to the direction of the arrow of the directionZ, and below (or down) corresponds to the opposite direction of thearrow of the direction Z.

FIG. 1 illustrates, in a flowchart diagram form, a method 10 forfabricating a semiconductor device 1A in accordance with one embodimentof the present disclosure. FIGS. 2 to 11 illustrate, in schematiccross-sectional view diagrams, part of a flow for fabricating thesemiconductor device 1A in accordance with one embodiment of the presentdisclosure. FIG. 12 illustrates, in a schematic top-view diagram, anintermediate semiconductor device 1A in accordance with one embodimentof the present disclosure. FIG. 13 is a schematic cross-sectional viewdiagram taken along a line A-A′ in FIG. 12 illustrating part of the flowfor fabricating the semiconductor device 1A in accordance with oneembodiment of the present disclosure.

With reference to FIGS. 1 to 5 , at step S11, a substrate 101 may beprovided, a first dielectric layer 111 may be formed on the substrate101, a second dielectric layer 113 may be formed on the first dielectriclayer 111, and a plurality of conductive features 130 may be formed onthe second dielectric layer 113.

With reference to FIG. 2 , the substrate 101 may include a bulksemiconductor substrate that is composed entirely of at least onesemiconductor material, a plurality of device elements (not show forclarity), a plurality of dielectric layers (not shown for clarity), anda plurality of conductive features (not show for clarity). The bulksemiconductor substrate may be formed of, for example, an elementarysemiconductor, such as silicon or germanium; a compound semiconductor,such as silicon germanium, silicon carbide, gallium arsenide, galliumphosphide, indium phosphide, indium arsenide, indium antimonide, orother III-V compound semiconductor or II-VI compound semiconductor; orcombinations thereof.

In some embodiments, the substrate 101 may include asemiconductor-on-insulator structure which consists of, from bottom totop, a handle substrate, an insulator layer, and a topmost semiconductormaterial layer. The handle substrate and the topmost semiconductormaterial layer may be formed of the same material as the bulksemiconductor substrate aforementioned. The insulator layer may be acrystalline or non-crystalline dielectric material such as an oxideand/or nitride. For example, the insulator layer may be a dielectricoxide such as silicon oxide. For another example, the insulator layermay be a dielectric nitride such as silicon nitride or boron nitride.For yet another example, the insulator layer may include a stack of adielectric oxide and a dielectric nitride such as a stack of, in anyorder, silicon oxide and silicon nitride or boron nitride. The insulatorlayer may have a thickness between about 10 nm and 200 nm.

With reference to FIG. 2 , the plurality of device elements may beformed on the bulk semiconductor substrate or the topmost semiconductormaterial layer. Some portions of the plurality of device elements may beformed in the bulk semiconductor substrate or the topmost semiconductormaterial layer. The plurality of device elements may be transistors suchas complementary metal-oxide-semiconductor transistors,metal-oxide-semiconductor field-effect transistors, finfield-effect-transistors, the like, or a combination thereof.

With reference to FIG. 2 , the plurality of dielectric layers may beformed on the bulk semiconductor substrate or the topmost semiconductormaterial layer and cover the plurality of device elements. In someembodiments, the plurality of dielectric layers may be formed of, forexample, silicon oxide, borophosphosilicate glass, undoped silicateglass, fluorinated silicate glass, low-k dielectric materials, the like,or a combination thereof. The low-k dielectric materials may have adielectric constant less than 3.0 or even less than 2.5. In someembodiments, the low-k dielectric materials may have a dielectricconstant less than 2.0. The plurality of dielectric layers may be formedby deposition processes such as chemical vapor deposition,plasma-enhanced chemical vapor deposition, or the like. Planarizationprocesses may be performed after the deposition processes to removeexcess material and provide a substantially flat surface for subsequentprocessing steps.

With reference to FIG. 2 , the plurality of conductive features mayinclude interconnect layers and conductive vias. The interconnect layersmay be separated from each other and may be horizontally disposed in theplurality of dielectric layers along the direction Z. The conductivevias may connect adjacent interconnect layers along the direction Z, andadjacent device element and interconnect layer. In some embodiments, theconductive vias may improve heat dissipation and may provide structuresupport. In some embodiments, the plurality of conductive features maybe formed of, for example, tungsten, cobalt, zirconium, tantalum,titanium, aluminum, ruthenium, copper, metal carbides (e.g., tantalumcarbide, titanium carbide, tantalum magnesium carbide), metal nitrides(e.g., titanium nitride), transition metal aluminides, or a combinationthereof. The plurality of conductive features may be formed during theformation of the plurality of dielectric layers.

In some embodiments, the plurality of device elements and the pluralityof conductive features may together configure functional units in thesubstrate 101. A functional unit, in the description of the presentdisclosure, generally refers to functionally related circuitry that hasbeen partitioned for functional purposes into a distinct unit. In someembodiments, functional units may be typically highly complex circuitssuch as processor cores, memory controllers, or accelerator units. Insome other embodiments, the complexity and functionality of a functionalunit may be more or less complex.

With reference to FIG. 2 , in some embodiments, the first dielectriclayer 111 may be formed of for example, fluorosilicate glass,borophosphosilicate glass, a spin-on low-k dielectric layer, a chemicalvapor deposition low-k dielectric layer, or a combination thereof. Insome embodiments, the first dielectric layer 111 may include aself-planarizing material such as a spin-on glass or a spin-on low-kdielectric material such as SiLK™. The use of a self-planarizingdielectric material may avoid the need to perform a subsequentplanarizing step. In some embodiments, the first dielectric layer 111may be formed by a deposition process including, for example, chemicalvapor deposition, plasma enhanced chemical vapor deposition,evaporation, or spin-on coating.

With reference to FIG. 2 , in some embodiments, the second dielectriclayer 113 may be, for example, silicon nitride, silicon oxide nitride,silicon oxynitride, the like, or a combination thereof. The seconddielectric layer 113 may be formed by, for example, chemical vapordeposition, plasma enhanced chemical vapor deposition, or otherapplicable deposition process. In some embodiments, the seconddielectric layer 113 may serve as a barrier layer to prevent moistureentering the underlying layers (e.g., the first dielectric layer 111 andthe substrate 101). In some embodiments, the thickness T1 of the firstdielectric layer 111 is greater than the thickness T2 of the seconddielectric layer 113.

With reference to FIG. 2 , a layer of first material 501 may be formedon the second dielectric layer 113. The first material 501 may be, forexample, titanium, titanium nitride, tantalum, tantalum nitride, or thelike. The layer of first material 501 may be formed by, for example,chemical vapor deposition, physical vapor deposition, sputtering, or thelike. A layer of second material 503 may be formed on the layer of firstmaterial 501. The second material 503 may be, for example, copper, acopper alloy, silver, gold, tungsten, aluminum, nickel, or the like. Thelayer of second material 503 may be formed by, for example, physicalvapor deposition, sputtering, or the like. A layer of third material 505may be formed on the layer of second material 503. In some embodiments,the third material 505 and the first material 501 may include the samematerial. In some embodiments, the third material 505 may be, forexample, titanium, titanium nitride, tantalum, tantalum nitride, or thelike. The third material 505 may be formed by, for example, chemicalvapor deposition, physical vapor deposition, sputtering, or the like.

With reference to FIG. 2 , a first mask layer 511 may be formed on thelayer of third material 505. The first mask layer 511 may be aphotoresist layer and may include the pattern of the plurality ofconductive features 130.

With reference to FIG. 3 , an etch process, such as an anisotropic dryetch process, may be performed to remove portions of the first material501, the second material 503, and the third material 505. After the etchprocess, the remaining first material 501 may be referred to as aplurality of bottom barrier layers 131, the remaining second material503 may be referred to as a plurality of middle conductive layers 135,and the remaining third material 505 may be referred to as a pluralityof top barrier layers 133. In some embodiments, the etch process may bea multi-step etch process and may be anisotropic.

For brevity, clarity, and convenience of description, only one bottombarrier layer 131, one middle conductive layer 135, and one top barrierlayer 133 are described. In some embodiments, the thickness T3 of thebottom barrier layer 131 and the thickness T4 of the top barrier layer133 may be about the same. In some embodiments, the thickness T3 of thebottom barrier layer 131 may be greater than the thickness T4 of the topbarrier layer 133. In some embodiments, the thickness T5 of the middleconductive layer 135 may be greater than the thickness T3 of the bottombarrier layer 131 or the thickness T4 of the top barrier layer 133.

With reference to FIG. 4 , a layer of fourth material 507 may beconformally formed over the intermediate semiconductor deviceillustrated in FIG. 3 . The fourth material 507 may be, for example,titanium, titanium nitride, tantalum, tantalum nitride, or the like. Thelayer of fourth material 507 may be formed by, for example, atomic layerdeposition, chemical vapor deposition, physical vapor deposition,sputtering, or the like. In some embodiments, the fourth material 507and the top barrier layer 133 may include the same material.

With reference to FIG. 5 , an etch process, such as an anisotropic dryetch process, may be performed to remove portions of the fourth material507. After the etch process, the remaining fourth material 507 may bereferred to as a plurality of spacer barriers 137. The plurality ofspacer barriers 137 may be formed to cover the sidewalls 133SW of thetop barrier layers 133, the sidewalls 135SW of the middle conductivelayers 135, and the sidewalls 131SW of the bottom barrier layer 131.

The plurality of spacer barriers 137, the plurality of top barrierlayers 133, the plurality of middle conductive layers 135, and theplurality of bottom barrier layers 131 together configure the pluralityof conductive features 130.

With reference to FIG. 1 and FIGS. 6 to 9 , at step S13, a middledielectric layer 115 may be formed on the second dielectric layer 113and surrounding the plurality of conductive features 130, and adecoupling unit 121 may be formed in the middle dielectric layer 115.

With reference to FIG. 6 , the middle dielectric layer 115 may be formedon the second dielectric layer 113 and cover the plurality of conductivefeatures 130. A planarization process, such as chemical mechanicalpolishing, may be performed until the top surfaces of the plurality ofconductive features 130 are exposed to remove excess material andprovide a substantially flat surface for subsequent processing steps. Insome embodiments, the middle dielectric layer 115 may be formed of amaterial having different etching rate with respect to the seconddielectric layer 113. In some embodiments, the middle dielectric layer115 may be formed of for example, silicon oxide, silicon nitride,silicon oxynitride, silicon nitride oxide, fluorosilicate glass,borophosphosilicate glass, or a combination thereof. In someembodiments, the middle dielectric layer 115 may be formed by, forexample, chemical vapor deposition, plasma enhanced chemical vapordeposition, or other applicable deposition process.

It should be noted that, in the description of the present disclosure, asurface of an element (or a feature) located at the highest verticallevel along the direction Z is referred to as a top surface of theelement (or the feature). A surface of an element (or a feature) locatedat the lowest vertical level along the direction Z is referred to as abottom surface of the element (or the feature).

With reference to FIG. 6 , a second mask layer 513 may be formed on themiddle dielectric layer 115. In some embodiments, the middle dielectriclayer 115 may be a photoresist layer and may include the pattern of thedecoupling unit 121.

With reference to FIG. 7 , an anisotropic etch process may be performedto remove portions of the middle dielectric layer 115 and concurrentlyform an opening 521. In some embodiments, the anisotropic etch processmay be an anisotropic dry etching process. In some embodiments, the etchrate ratio of the middle dielectric layer 115 to the second dielectriclayer 113 may be between about 100:1 and about 1.05:1, between about15:1 and about 2:1, or between about 10:1 and about 2:1 during theanisotropic etch process.

With reference to FIG. 8 , an expansion etch process may be performed toexpand the opening 521 into an expanded opening 523. In someembodiments, the expansion etch process may be an isotropic etchprocess. In some embodiments, the expansion etch process may be a wetetch process. In some embodiments, the etch rate ratio of the middledielectric layer 115 to the second dielectric layer 113 may be betweenabout 100:1 and about 1.05:1, between about 15:1 and about 2:1, orbetween about 10:1 and about 2:1 during the expansion etch process. Insome embodiments, the sidewall of the expanded opening 523 may becurved.

With reference to FIG. 9 , the second mask layer 513 may be removed, aninsulating material may be deposited to completely fill the expandedopening 523, and a planarization process, such as chemical mechanicalpolishing, may be subsequently performed until the top surfaces of theplurality of conductive features 130 are exposed to remove excessmaterial, provide a substantially flat surface for subsequent processingsteps, and concurrently form the decoupling unit 121. In someembodiments, the decoupling unit 121 may have a bottle-shapedcross-sectional profile. In some embodiments, the insulating material tobe formed the decoupling unit 121 may be, for example, a porous low-kmaterial.

In some embodiments, the insulating material to be formed the decouplingunit 121 may be an energy-removable material. The energy-removablematerial may include a material such as a thermal decomposable material,a photonic decomposable material, an e-beam decomposable material, or acombination thereof. For example, the energy-removable material mayinclude a base material and a decomposable porogen material that issacrificially removed upon being exposed to an energy source. The basematerial may include a methylsilsesquioxane based material. Thedecomposable porogen material may include a porogen organic compoundthat provides porosity to the base material of the energy-removablematerial. An energy treatment may be performed after the planarizationprocess by applying an energy source. The energy source may includeheat, light, or a combination thereof. When heat is used as the energysource, a temperature of the energy treatment may be between about 800°C. and about 900° C. When light is used as the energy source, anultraviolet light may be applied. The energy treatment may remove thedecomposable porogen material from the energy-removable material togenerate empty spaces (pores), with the base material remaining inplace. The empty spaces (pores) may reduce the dielectric constant ofthe decoupling unit 121.

With reference to FIG. 9 , the decoupling unit 121 may be formed betweenthe plurality of conductive features 130. In some embodiments, thedecoupling unit 121 having low dielectric constant may implement adecoupling function. In some embodiments, the decoupling unit 121 mayreduce parasitic capacitance of the plurality of conductive features130.

With reference to FIG. 1 and FIGS. 10 to 13 , at step S15, a thirddielectric layer 117 may be formed on the middle dielectric layer 115,and a fourth dielectric layer 119 may be formed on the third dielectriclayer 117 to configure a first tier structure 100, and afirst-tier-alignment mark 611 and a first-tier-alignment mark 711 may beformed in the first tier structure 100.

With reference to FIG. 10 , in some embodiments, the third dielectriclayer 117 may be formed of for example, fluorosilicate glass,borophosphosilicate glass, a spin-on low-k dielectric layer, a chemicalvapor deposition low-k dielectric layer, or a combination thereof. Insome embodiments, the third dielectric layer 117 may include aself-planarizing material such as a spin-on glass or a spin-on low-kdielectric material such as SiLK™. The use of a self-planarizingdielectric material may avoid the need to perform a subsequentplanarizing step. In some embodiments, the third dielectric layer 117may be formed by a deposition process including, for example, chemicalvapor deposition, plasma enhanced chemical vapor deposition,evaporation, or spin-on coating. In some embodiments, the thirddielectric layer 117 and the first dielectric layer 111 may be formed ofthe same material.

With reference to FIG. 10 , in some embodiments, the fourth dielectriclayer 119 may be, for example, silicon nitride, silicon oxide nitride,silicon oxynitride, the like, or a combination thereof. The fourthdielectric layer 119 may be formed by, for example, chemical vapordeposition, plasma enhanced chemical vapor deposition, or otherapplicable deposition process. In some embodiments, the fourthdielectric layer 119 may serve as a barrier layer to prevent moistureentering the underlying layers (e.g., the third dielectric layer 117 andthe middle dielectric layer 115). In some embodiments, the thickness T6of the third dielectric layer 117 is greater than the thickness T7 ofthe fourth dielectric layer 119.

With reference to FIG. 10 , the first dielectric layer 111, the seconddielectric layer 113, the middle dielectric layer 115, the thirddielectric layer 117, and the fourth dielectric layer 119, thedecoupling unit 121, and the plurality of conductive features 130 maytogether configure the first tier structure 100.

With reference to FIG. 10 , a third mask layer 515 may be formed on thefirst tier structure 100. The third mask layer 515 may be a photoresistlayer and may include the pattern of the first-tier-alignment mark 611and the first-tier-alignment mark 711.

Due to the first-tier-alignment mark 611 and the first-tier-alignmentmark 711 being concurrently formed, only the formation of thefirst-tier-alignment mark 611 is described for brevity and clarity.

With reference to FIG. 11 , an etch process, such as an anisotropic dryetch process, may be performed to remove portions of the fourthdielectric layer 119, portions of the third dielectric layer 117, andportions of the decoupling unit 121 to form a mark opening 525. In someembodiments, the sidewall of the mark opening 525 may be tapered. Itshould be noted that the mark opening 525 is used for forming thefirst-tier-alignment mark 611 and the mark opening for forming thefirst-tier-alignment mark 711 is not shown in FIG. 11 for brevity andclarity.

With reference to FIGS. 12 and 13 , an insulating layer may be formed tocompletely fill the mark opening 525. The insulating layer may include afluorescence material. In some embodiments, the fluorescence materialmay be azobenzene. In some embodiments, the insulating layer may beformed by, for example, chemical vapor deposition. A planarizationprocess, such as chemical mechanical polishing, may be performed untilthe fourth dielectric layer 119 is exposed to remove excess material,provide a substantially flat surface for subsequent processing steps,and concurrently turn the insulating layer into the first-tier-alignmentmark 611 (and the first-tier-alignment mark 711). Due to the profile ofthe first-tier-alignment mark 611 is determined by the mark opening 525.The sidewall 611SW of the first-tier-alignment mark 611 may be tapered.

In some embodiments, the width W1 between the two valleys 121V of thesidewall 121SW of the decoupling unit 121 may be greater than the widthW2 of the top surface 611TS of the first-tier-alignment mark 611. Insome embodiments, the width W2 of the top surface 611TS of thefirst-tier-alignment mark 611 may be greater than the width W3 of thefirst-tier-alignment mark 611 at the interface between the middledielectric layer 115 and the third dielectric layer 117. In someembodiments, the width W3 of the first-tier-alignment mark 611 at theinterface between the middle dielectric layer 115 and the thirddielectric layer 117 may be greater than the width W4 of the bottomsurface 611BS of the first-tier-alignment mark 611. In some embodiments,the width W3 of the first-tier-alignment mark 611 at the interfacebetween the middle dielectric layer 115 and the third dielectric layer117 may be greater than the width W5 of the bottom surface 121BS of thedecoupling unit 121. In some embodiments, the width ratio between thewidth W1 and the width W5 may be between about 1.5:1 and about 1.1:1 orbetween about 1.3:1 and about 1.1:1.

The first-tier-alignment mark 611 (and the first-tier-alignment mark711) including fluorescence material may improve optical recognitionduring the following wafer fabrication process.

With reference to FIGS. 12 and 13 , in some embodiments, thefirst-tier-alignment mark 611 and the first-tier-alignment mark 711 maybe distant from each other. In some embodiments, thefirst-tier-alignment mark 611 and the first-tier-alignment mark 711 maybe formed in a mirror manner according to a first axis of symmetry S1 ina top-view perspective.

FIG. 14 illustrates, in a schematic top-view diagram, an intermediatesemiconductor device 1A in accordance with one embodiment of the presentdisclosure. FIG. 15 is a schematic cross-sectional view diagram takenalong a line A-A′ in FIG. 14 illustrating part of the flow forfabricating the semiconductor device 1A in accordance with oneembodiment of the present disclosure. FIG. 16 illustrates, in aschematic top-view diagram, an intermediate semiconductor device 1A inaccordance with one embodiment of the present disclosure. FIG. 17 is aschematic cross-sectional view diagram taken along a line A-A′ in FIG.16 illustrating part of the flow for fabricating the semiconductordevice 1A in accordance with one embodiment of the present disclosure.It should be noted that some elements are omitted in FIGS. 14, 16, and17 for clarity.

With reference to FIG. 1 and FIGS. 14 to 17 , at step S17, a second tierstructure 200, second-tier-alignment marks 613, 713, a third tierstructure 300, third-tier-alignment marks 615, 715, a fourth tierstructure 400, and fourth-tier-alignment marks 617, 717 may be formedover the first tier structure 100.

With reference to FIGS. 14 and 15 , the second tier structure 200 may beformed on the first tier structure 100. The second tier structure 200may include a first dielectric layer 211, a second dielectric layer 213,a middle dielectric layer 215, a third dielectric layer 217, a fourthdielectric layer 219, a plurality of conductive features 230, and adecoupling unit 221. The aforementioned elements of the second tierstructure 200 may be formed with a procedure similar to the first tierstructure 100, and descriptions thereof are not repeated herein. In someembodiments, the plurality of conductive features 230 may be deviatedfrom the plurality of conductive features 130. The decoupling unit 221may be formed between the plurality of conductive features 230. Thesecond-tier-alignment mark 613 may be formed on the decoupling unit 221with a procedure similar to the first-tier-alignment mark 611, anddescriptions thereof are not repeated herein.

With reference to FIGS. 16 and 17 , the third tier structure 300 may beformed on the second tier structure 200. The third-tier-alignment marks615, 715 may be formed on the decoupling units 321 of the third tierstructure 300, respectively and correspondingly. The fourth tierstructure 400 may be formed on the third tier structure 300. Thefourth-tier-alignment marks 617, 717 may be formed on the decouplingunits 421 of the fourth tier structure 400, respectively andcorrespondingly. The aforementioned elements may be formed with aprocedure similar to the second tier structure 200 and the decouplingunit 221, respectively and correspondingly, and descriptions thereof arenot repeated herein.

The first-tier-alignment mark 611, the second-tier-alignment mark 613,the third-tier-alignment mark 615, and the fourth-tier-alignment mark617 may be referred to as a first subset of solid alignment marks 610.The first-tier-alignment mark 711, the second-tier-alignment mark 713,the third-tier-alignment mark 715, and the fourth-tier-alignment mark717 may be referred to as a first subset of spaced alignment marks 710.

In some embodiments, the first-tier-alignment marks 611 may be lineshaped in a top-view perspective. The first-tier-alignment mark 611 mayextend along the direction Y.

In a cross-sectional perspective, the second-tier-alignment mark 613 maybe in the second tier structure 200 and may be deviated from thefirst-tier-alignment mark 611. In other words, the second-tier-alignmentmark 613 may not be directly above the first-tier-alignment mark 611. Ina top-view perspective, the second-tier-alignment mark 613 may be lineshaped. The second-tier-alignment mark 613 may extend along thedirection Y and may be separated from the first-tier-alignment mark 611along the direction X.

In a cross-sectional perspective, the third-tier-alignment mark 615 maybe in the third tier structure 300 and may be deviated from thesecond-tier-alignment mark 613. In other words, the third-tier-alignmentmark 615 may not be directly above the second-tier-alignment mark 613.In a top-view perspective, the third-tier-alignment mark 615 may be lineshaped. The third-tier-alignment mark 615 may extend along the directionY and may be separated from the second-tier-alignment mark 613 along thedirection X. The second-tier-alignment mark 613 may be between thefirst-tier-alignment mark 611 and the third-tier-alignment mark 615.

In a cross-sectional perspective, the fourth-tier-alignment mark 617 maybe in the fourth tier structure 400 and may be deviated from thethird-tier-alignment mark 615. In other words, the fourth-tier-alignmentmark 617 may not be directly above the third-tier-alignment mark 615. Ina top-view perspective, the fourth-tier-alignment mark 617 may be lineshaped. The fourth-tier-alignment mark 617 may extend along thedirection Y and may be separated from the third-tier-alignment mark 615along the direction X. The third-tier-alignment mark 615 may be disposedbetween the second-tier-alignment mark 613 and the fourth-tier-alignmentmark 617.

In some embodiments, the first-tier-alignment mark 611, thesecond-tier-alignment mark 613, the third-tier-alignment mark 615, andthe fourth-tier-alignment mark 617 may be aligned to each other alongthe direction Y. In some embodiments, the first-tier-alignment mark 611,the second-tier-alignment mark 613, the third-tier-alignment mark 615,and the fourth-tier-alignment mark 617 may not be aligned to each otheralong the direction Y.

In some embodiments, in a top-view perspective, the length L1 of thefirst-tier-alignment mark 611 and the width W2 of thefirst-tier-alignment mark 611 may be different. For example, the lengthL1 of the first-tier-alignment mark 611 may be greater than the width W2of the first-tier-alignment mark 611. In some embodiments, the length L1of the first-tier-alignment mark 611 and the width W2 of thefirst-tier-alignment mark 611 may be substantially the same.

In some embodiments, the lengths of the second-tier-alignment mark 613,the third-tier-alignment mark 615, the fourth-tier-alignment mark 617may be substantially the same as the length L1 of thefirst-tier-alignment mark 611. In some embodiments, the lengths of thesecond-tier-alignment mark 613, the third-tier-alignment mark 615, thefourth-tier-alignment mark 617 may be different from the length L1 ofthe first-tier-alignment mark 611. For example, the length L2 of thesecond-tier-alignment mark 613 may be the same as or different from thelength L1 of the first-tier-alignment mark 611.

In some embodiments, the widths of the second-tier-alignment mark 613,the third-tier-alignment mark 615, the fourth-tier-alignment mark 617may be substantially the same as the width W2 of thesecond-tier-alignment mark 613. In some embodiments, the widths of thesecond-tier-alignment mark 613, the third-tier-alignment mark 615, thefourth-tier-alignment mark 617 may be different from the width W2 of thefirst-tier-alignment mark 611. For example, the width W6 of thesecond-tier-alignment mark 613 may be the same as or different from thewidth W2 of the first-tier-alignment mark 611.

In some embodiments, in a top-view perspective, the width W2 of thefirst-tier-alignment mark 611 and the distance D1 between thefirst-tier-alignment mark 611 and the second-tier-alignment mark 613 maybe different. For example, the width W2 of the first-tier-alignment mark611 may be greater than the distance D1 between the first-tier-alignmentmark 611 and the second-tier-alignment mark 613. In some embodiments,the width W2 of the second-tier-alignment mark 613 and the distance D1between the first-tier-alignment mark 611 and the second-tier-alignmentmark 613 may be substantially the same.

In some embodiments, in a top-view perspective, the distances D1, D2, D3between the first-tier-alignment mark 611, the second-tier-alignmentmark 613, the third-tier-alignment mark 615, and thefourth-tier-alignment mark 617 may be substantially the same. In someembodiments, the distances D1, D2, D3 between the first-tier-alignmentmark 611, the second-tier-alignment mark 613, the third-tier-alignmentmark 615, and the fourth-tier-alignment mark 617 may be different. Forexample, the distance D1 between the first-tier-alignment mark 611 andthe second-tier-alignment mark 613 may be greater than or less than thedistance D2 between the second-tier-alignment mark 613 and thethird-tier-alignment mark 615.

The first-tier-alignment mark 611, the second-tier-alignment mark 613,the third-tier-alignment mark 615, and the fourth-tier-alignment mark617 may include a fluorescence material. In some embodiments, thefluorescence material may be azobenzene. The first-tier-alignment mark611, the second-tier-alignment mark 613, the third-tier-alignment mark615, and the fourth-tier-alignment mark 617 including the fluorescencematerial may improve optical recognition during the wafer fabricationprocess.

With reference to FIGS. 16 and 17 , the first subset of spaced alignmentmarks 710 and the first subset of solid alignment marks 610 may beformed in a mirror manner according to the first axis of symmetry S1.Detailedly, the first-tier-alignment mark 711 and thefirst-tier-alignment mark 611 may be formed in the mirror manneraccording to the first axis of symmetry S1. The second-tier-alignmentmark 713 and the second-tier-alignment mark 613 may be formed in themirror manner according to the first axis of symmetry S1. Thethird-tier-alignment mark 715 and the third-tier-alignment mark 615 maybe formed in the mirror manner according to the first axis of symmetryS1. The fourth-tier-alignment mark 717 and the fourth-tier-alignmentmark 617 may be disposed in the mirror manner according to the firstaxis of symmetry S1.

The first-tier-alignment mark 711, the second-tier-alignment mark 713,the third-tier-alignment mark 715, and the fourth-tier-alignment mark717 may include a fluorescence material. In some embodiments, thefluorescence material may be azobenzene. The first-tier-alignment mark711, the second-tier-alignment mark 713, the third-tier-alignment mark715, and the fourth-tier-alignment mark 717 including the fluorescencematerial may improve optical recognition during the wafer fabricationprocess.

FIG. 18 illustrates, in a schematic top-view diagram, a semiconductordevice 1B in accordance with another embodiment of the presentdisclosure. FIG. 19 is a schematic cross-sectional view diagram takenalong lines A-A′ and B-B′ in FIG. 18 . It should be noted that someelements are omitted in FIGS. 18 and 19 for clarity.

With reference to FIGS. 18 and 19 , the semiconductor device 1B may havea structure similar to that illustrated in FIGS. 16 and 17 . The same orsimilar elements in FIGS. 18 and 19 as in FIGS. 16 and 17 have beenmarked with similar reference numbers and duplicative descriptions havebeen omitted.

With reference to FIGS. 18 and 19 , the semiconductor device 1B mayinclude a second subset of solid alignment marks 620. The first subsetof solid alignment marks 610 and a second subset of solid alignmentmarks 620 may configure a first set of solid alignment marks 600-1. Thesecond subset of solid alignment marks 620 may include afirst-tier-alignment mark 621, a second-tier-alignment mark 623, athird-tier-alignment mark 625, and a fourth-tier-alignment mark 627.

With reference to FIGS. 18 and 19 , in some embodiments, thefirst-tier-alignment mark 621 may be line shaped in a top-viewperspective. The first-tier-alignment mark 621 may extend along thedirection Y. The first-tier-alignment mark 621 may be aligned with thethird-tier-alignment mark 615 along the direction X and separated fromthe third-tier-alignment mark 615 along the direction Y. In across-sectional perspective, the first-tier-alignment mark 621 may bedisposed in the first tier structure 100 and on the correspondingdecoupling unit 121.

In a cross-sectional perspective, the second-tier-alignment mark 623 maybe disposed in the second tier structure 200, deviated from thefirst-tier-alignment mark 621, and on the corresponding decoupling unit221. In other words, the second-tier-alignment mark 623 may not bedirectly above the first-tier-alignment mark 621. In a top-viewperspective, the second-tier-alignment mark 623 may be line shaped. Thesecond-tier-alignment mark 623 may extend along the direction Y and maybe separated from the first-tier-alignment mark 621 along the directionX. The second-tier-alignment mark 623 may be aligned with thefourth-tier-alignment mark 617 along the direction X and separated fromthe fourth-tier-alignment mark 617 along the direction Y.

In a cross-sectional perspective, the third-tier-alignment mark 625 maybe disposed in the third tier structure 300, deviated from thesecond-tier-alignment mark 623, and on the corresponding decoupling unit321. In other words, the third-tier-alignment mark 625 may not bedirectly above the second-tier-alignment mark 623. In a top-viewperspective, the third-tier-alignment mark 625 may be line shaped. Thethird-tier-alignment mark 625 may extend along the direction Y and maybe distant from the first-tier-alignment mark 621 along the direction X.The third-tier-alignment mark 625 may be aligned with thefirst-tier-alignment mark 621 along the direction X and separated fromthe first-tier-alignment mark 621 along the direction Y.

In a cross-sectional perspective, the fourth-tier-alignment mark 627 maybe disposed in the fourth tier structure 400, deviated from thethird-tier-alignment mark 625, and on the corresponding decoupling unit421. In other words, fourth-tier-alignment mark 627 may not be directlyabove the third-tier-alignment mark 625. In a top-view perspective, thefourth-tier-alignment mark 627 may be line shaped. Thefourth-tier-alignment mark 627 may extend along the direction Y and maybe separated from the third-tier-alignment mark 625 along the directionX. For example, the fourth-tier-alignment mark 627 may be disposedbetween the first-tier-alignment mark 621 and the third-tier-alignmentmark 625. For another example, the fourth-tier-alignment mark 627 may bealigned with the second-tier-alignment mark 613 along the direction X.The fourth-tier-alignment mark 627 may be separated from thesecond-tier-alignment mark 613 along the direction Y.

In some embodiments, the first-tier-alignment mark 621, thesecond-tier-alignment mark 623, the third-tier-alignment mark 625, andthe fourth-tier-alignment mark 627 may be aligned to each other alongthe direction Y. In some embodiments, the first-tier-alignment mark 621,the second-tier-alignment mark 623, the third-tier-alignment mark 625,and the fourth-tier-alignment mark 627 may not be aligned to each otheralong the direction Y.

In some embodiments, the width W7 of the first-tier-alignment mark 621and the width W2 of the first-tier-alignment mark 611 may besubstantially the same. In some embodiments, the width W7 of thefirst-tier-alignment mark 621 and the width W2 of thefirst-tier-alignment mark 611 may be different. In some embodiments, thelength L3 of the first-tier-alignment mark 621 and the length L1 of thefirst-tier-alignment mark 611 may be substantially the same. In someembodiments, the length L3 of the first-tier-alignment mark 621 and thelength L1 of the first-tier-alignment mark 611 may be different.

In some embodiments, the lengths of the second-tier-alignment mark 623,the third-tier-alignment mark 625, the fourth-tier-alignment mark 627may be substantially the same as the length L3 of thefirst-tier-alignment mark 621. In some embodiments, the lengths of thesecond-tier-alignment mark 623, the third-tier-alignment mark 625, thefourth-tier-alignment mark 627 may be different from the length L3 ofthe first-tier-alignment mark 621. In some embodiments, the widths ofthe second-tier-alignment mark 623, the third-tier-alignment mark 625,the fourth-tier-alignment mark 627 may be substantially the same as thewidth W3 of the first-tier-alignment mark 621. In some embodiments, thewidths of the second-tier-alignment mark 623, the third-tier-alignmentmark 625, the fourth-tier-alignment mark 627 may be different from thewidth W3 of the first-tier-alignment mark 621.

In some embodiments, the length L1 of the first-tier-alignment mark 611and the distance G1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621 may be substantially the same. In someembodiments, the length L1 of the first-tier-alignment mark 611 and thedistance G1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621 may be different. For example, the lengthL1 of the first-tier-alignment mark 611 may be greater than the distanceG1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621.

In some embodiments, the width W1 of the first-tier-alignment mark 611and the distance G1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621 may be substantially the same. In someembodiments, the width W1 of the first-tier-alignment mark 611 and thedistance G1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621 may be different. For example, the widthW1 of the first-tier-alignment mark 621 may be greater than the distanceG1 between the third-tier-alignment mark 615 and thefirst-tier-alignment mark 621.

In some embodiments, the first-tier-alignment mark 621, thesecond-tier-alignment mark 623, the third-tier-alignment mark 625, andthe fourth-tier-alignment mark 627 may include a fluorescence material.In some embodiments, the fluorescence material may be azobenzene. Thefirst-tier-alignment mark 621, the second-tier-alignment mark 623, thethird-tier-alignment mark 625, and the fourth-tier-alignment mark 627including the fluorescence material may improve optical recognitionduring the wafer fabrication process.

FIG. 20 illustrates, in a schematic top-view diagram, a semiconductordevice 1C in accordance with another embodiment of the presentdisclosure. FIG. 21 is a schematic cross-sectional view diagram takenalong lines A-A′ and B-B′ in FIG. 20 . It should be noted that someelements are omitted in FIGS. 20 and 21 for clarity.

With reference to FIGS. 20 and 21 , the semiconductor device 1C may havea structure similar to that illustrated in FIGS. 16 and 17 . The same orsimilar elements in FIGS. 20 and 21 as in FIGS. 16 and 17 have beenmarked with similar reference numbers and duplicative descriptions havebeen omitted.

With reference to FIGS. 20 and 21 , the semiconductor device 1C mayinclude a third subset of solid alignment marks 630. The third subset ofsolid alignment marks 630 and the first subset of solid alignment marks610 may be disposed in a mirror manner according to the second axis ofsymmetry S2. Detailedly, the third subset of solid alignment marks 630may include a first-tier-alignment mark 631, a second-tier-alignmentmark 633, a third-tier-alignment mark 635, and a fourth-tier-alignmentmark 637. The first-tier-alignment mark 631 and the first-tier-alignmentmark 611 may be disposed in the mirror manner according to the secondaxis of symmetry S2. The second-tier-alignment mark 633 and thesecond-tier-alignment mark 613 may be disposed in the mirror manneraccording to the second axis of symmetry S2. The third-tier-alignmentmark 635 and the third-tier-alignment mark 615 may be disposed in themirror manner according to the second axis of symmetry S2. Thefourth-tier-alignment mark 637 and the fourth-tier-alignment mark 617may be disposed in the mirror manner according to the second axis ofsymmetry S2.

FIG. 22 illustrates, in a schematic top-view diagram, a semiconductordevice 1D in accordance with another embodiment of the presentdisclosure. FIG. 23 is a schematic cross-sectional view diagram takenalong lines A-A′ and B-B′ in FIG. 22 . FIG. 24 is a schematiccross-sectional view diagram taken along lines C-C′ and D-D′ in FIG. 22. It should be noted that some elements are omitted in FIGS. 22 to 24for clarity.

With reference to FIGS. 22 to 24 , the semiconductor device 1D may havea structure similar to that illustrated in FIGS. 20 and 21 . The same orsimilar elements in FIGS. 22 to 24 as in FIGS. 20 and 21 have beenmarked with similar reference numbers and duplicative descriptions havebeen omitted.

With reference to FIGS. 22 to 24 , the semiconductor device 1D mayinclude a second subset of solid alignment marks 620, a third subset ofsolid alignment marks 630, a fourth subset of solid alignment marks 640,a second subset of spaced alignment marks 720, a third subset of spacedalignment marks 730, and a fourth subset of spaced alignment marks 740.The first subset of solid alignment marks 610 and the second subset ofsolid alignment marks 620 together configure a first set of solidalignment marks 600-1. The third subset of solid alignment marks 630 andthe fourth subset of solid alignment marks 640 together configure asecond set of solid alignment marks 600-2. The first subset of spacedalignment marks 710 and the second subset of spaced alignment marks 720together configure a first set of spaced alignment marks 700-1. Thethird subset of spaced alignment marks 730 and the fourth subset ofspaced alignment marks 740 together configure a second set of spacedalignment marks 700-2.

With reference to FIGS. 22 to 24 , the second subset of solid alignmentmarks 620 may be disposed in a manner similar to that illustrated inFIGS. 18 and 19 , and descriptions thereof are not repeated herein. Thethird subset of solid alignment marks 630 may be disposed in a mannersimilar to that illustrated in FIGS. 20 and 21 , and descriptionsthereof are not repeated herein.

With reference to FIGS. 22 to 24 , the second subset of spaced alignmentmarks 720 may include a first-tier-alignment mark 721, asecond-tier-alignment mark 723, a third-tier-alignment mark 725, and afourth-tier-alignment mark 727. The second subset of spaced alignmentmarks 720 and the second subset of solid alignment marks 620 may bedisposed in a mirror manner according to the first axis of symmetry S1.

With reference to FIGS. 22 to 24 , the third subset of spaced alignmentmarks 730 may include a first-tier-alignment mark 731, asecond-tier-alignment mark 733, a third-tier-alignment mark 735, and afourth-tier-alignment mark 737. The third subset of spaced alignmentmarks 730 may be disposed in a mirror manner of the first subset ofspaced alignment marks 710 according to the third axis of symmetry S3 orthe third subset of spaced alignment marks 730 may be disposed in amirror manner of the third subset of solid alignment marks 630 accordingto the first axis of symmetry S1, and descriptions thereof are notrepeated herein.

With reference to FIGS. 22 to 24 , the fourth subset of spaced alignmentmarks 740 may include a first-tier-alignment mark 741, asecond-tier-alignment mark 743, a third-tier-alignment mark 745, and afourth-tier-alignment mark 747. The fourth subset of spaced alignmentmarks 740 may be disposed in a mirror manner of the second subset ofspaced alignment marks 720 according to the third axis of symmetry S3 orthe fourth subset of spaced alignment marks 740 may be disposed in amirror manner of the fourth subset of solid alignment marks 640according to the first axis of symmetry S1, and descriptions thereof arenot repeated herein.

One aspect of the present disclosure provides a semiconductor deviceincluding a first tier structure including a plurality of conductivefeatures of the first tier structure positioned over a substrate, and adecoupling unit of the first tier structure positioned between theplurality of conductive features of the first tier structure; a firstset of solid alignment marks including a first-tier-alignment markpositioned on the decoupling unit of the first tier structure, andincluding a fluorescence material; a second tier structure positioned onthe first tier structure and including a plurality of conductivefeatures of the second tier structure positioned over and deviated fromthe plurality of conductive features of the first tier structure, and adecoupling unit of the second tier structure positioned over the firsttier structure, and positioned between the plurality of conductivefeatures of the second tier structure; and a first set of spacedalignment marks including a second-tier-alignment mark positioned on thedecoupling unit of the second tier structure, and including afluorescence material. The decoupling units of the first tier structureand the second tier structure include a low-k dielectric material andrespectively include a bottle-shaped cross-sectional profile.

Another aspect of the present disclosure provides a semiconductor deviceincluding a first tier structure positioned on a substrate andincluding: a plurality of conductive features of the first tierstructure positioned over the substrate, and a decoupling unit of thefirst tier structure positioned between the plurality of conductivefeatures of the first tier structure, and including a bottle-shapedcross-sectional profile; a first set of solid alignment marks including:a first-tier-alignment mark of the first set of solid alignment markspositioned on the decoupling unit of the first tier structure; a firstset of spaced alignment marks including: a first-tier-alignment mark ofthe first set of spaced alignment marks positioned in a mirror manner ofthe first-tier-alignment mark of the first set of solid alignment marksaccording to a first axis of symmetry. The first-tier-alignment mark ofthe first set of solid alignment marks and the first-tier-alignment markof the first set of spaced alignment marks include a fluorescencematerial. The decoupling unit of the first tier structure includes alow-k dielectric material.

Another aspect of the present disclosure provides a method forfabricating a semiconductor device including forming a first tierstructure over a substrate and including: a plurality of conductivefeatures over the substrate, and a decoupling unit between the pluralityof conductive features; forming a first set of solid alignment marksincluding a first-tier-alignment mark on the decoupling unit of thefirst tier structure; forming a second tier structure over the firsttier structure and including: a plurality of conductive features overthe first tier structure, and a decoupling unit between the plurality ofconductive features; and forming a first set of spaced alignment marksincluding a second-tier-alignment mark on the decoupling unit of thesecond tier structure. The first-tier-alignment mark and thesecond-tier-alignment mark includes a fluorescence material. Thedecoupling units of the first tier structure and the second tierstructure include a low-k dielectric material.

Due to the design of the semiconductor device of the present disclosure,the first-tier-alignment marks 611, 621, 631, 641, 711, 721, 731, 741,the second-tier-alignment marks 613, 623, 633, 643, 713, 723, 733, 743,the third-tier-alignment marks 615, 625, 635, 645, 715, 725, 735, 745,and the fourth-tier-alignment marks 617, 627, 637, 647, 717, 727, 737,747 including the fluorescence material may improve optical recognitionduring the wafer fabrication process. As a result, the yield offabricating the semiconductor device 1A, 1B, 1C, 1D may be improved. Inaddition, the decoupling units 121, 221, 321, 421 may reduce parasiticcapacitance of the plurality of conductive features 130, 230, 330, 430.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. For example,many of the processes discussed above can be implemented in differentmethodologies and replaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, and steps.

What is claimed is:
 1. A semiconductor device, comprising: a first tierstructure positioned on a substrate and comprising: a plurality ofconductive features of the first tier structure positioned over thesubstrate; and a decoupling unit of the first tier structure positionedbetween the plurality of conductive features of the first tierstructure, and comprising a bottle-shaped cross-sectional profile; afirst set of solid alignment marks comprising: a first-tier-alignmentmark of the first set of solid alignment marks positioned on thedecoupling unit of the first tier structure; a first set of spacedalignment marks comprising: a first-tier-alignment mark of the first setof spaced alignment marks positioned in a mirror manner of thefirst-tier-alignment mark of the first set of solid alignment marksaccording to a first axis of symmetry; wherein the first-tier-alignmentmark of the first set of solid alignment marks and thefirst-tier-alignment mark of the first set of spaced alignment markscomprise a fluorescence material; wherein the decoupling unit of thefirst tier structure comprises a low-k dielectric material.
 2. Thesemiconductor device of claim 1, wherein the fluorescence materialcomprises azobenzene.
 3. The semiconductor device of claim 2, whereinthe first-tier-alignment mark of the first set of solid alignment marksis line shaped in a top-view perspective and extends along a firstdirection; wherein the first axis of symmetry is slanted with respectiveto the first direction.
 4. The semiconductor device of claim 3, whereinthe first set of solid alignment marks comprises a second-tier-alignmentmark positioned above and deviated from the first-tier-alignment mark ofthe first set of solid alignment marks, and comprising azobenzene. 5.The semiconductor device of claim 4, wherein the second-tier-alignmentmark of the first set of solid alignment marks is line shaped, extendingalong the first direction, and separated from the first-tier-alignmentmark of the first set of solid alignment marks along a second directionperpendicular to the first direction.
 6. The semiconductor device ofclaim 5, wherein a length of the first-tier-alignment mark of the firstset of solid alignment marks and a length of the second-tier-alignmentmark of the first set of solid alignment marks are substantially thesame.
 7. The semiconductor device of claim 6, wherein a width of thefirst-tier-alignment mark of the first set of solid alignment marks anda width of the second-tier-alignment mark of the first set of solidalignment marks are substantially the same.
 8. The semiconductor deviceof claim 7, wherein the width of the first-tier-alignment mark of thefirst set of solid alignment marks is different from a distance betweenthe first-tier-alignment mark of the first set of solid alignment marksand the second-tier-alignment mark of the first set of solid alignmentmarks.
 9. The semiconductor device of claim 8, wherein the first tierstructure comprises: a first dielectric layer positioned on thesubstrate; a second dielectric layer positioned on the first dielectriclayer; a middle dielectric layer positioned on the second dielectriclayer; a third dielectric layer positioned on the middle dielectriclayer; and a fourth dielectric layer positioned on the third dielectriclayer; wherein the decoupling unit of the first tier structure ispositioned in the middle dielectric layer and on the second dielectriclayer; wherein the first-tier-alignment mark of the first set of solidalignment marks is positioned along the fourth dielectric layer and thethird dielectric layer, extending to the middle dielectric layer, and onthe decoupling unit of the first tier structure.
 10. The semiconductordevice of claim 8, wherein the first dielectric layer and the thirddielectric layer comprise the same material.
 11. The semiconductordevice of claim 10, wherein the second dielectric layer and the fourthdielectric layer comprise the same material.
 12. The semiconductordevice of claim 11, wherein the plurality of conductive features of thefirst tier structure respectively comprises: a bottom barrier layerpositioned on the second dielectric layer; a middle conductive layerpositioned on the bottom barrier layer; a top barrier layer positionedon the middle conductive layer; and a spacer barrier positioned onsidewalls of the bottom barrier layer, the middle conductive layer, andthe top barrier layer.
 13. A method for fabricating a semiconductordevice, comprising: forming a first tier structure over a substrate andcomprising: a plurality of conductive features over the substrate, and adecoupling unit between the plurality of conductive features; forming afirst set of solid alignment marks comprising a first-tier-alignmentmark on the decoupling unit of the first tier structure; forming asecond tier structure over the first tier structure and comprising: aplurality of conductive features over the first tier structure, and adecoupling unit between the plurality of conductive features; andforming a first set of spaced alignment marks comprising asecond-tier-alignment mark on the decoupling unit of the second tierstructure; wherein the first-tier-alignment mark and thesecond-tier-alignment mark comprises a fluorescence material; whereinthe decoupling units of the first tier structure and the second tierstructure comprise a low-k dielectric material.
 14. The method forfabricating the semiconductor device of claim 13, wherein thefluorescence material comprises azobenzene.
 15. The method forfabricating the semiconductor device of claim 14, wherein the decouplingunit of the first tier structure comprises a bottle-shaped crosssectional profile.
 16. The method for fabricating the semiconductordevice of claim 15, wherein forming the first tier structure over thesubstrate comprising: forming a first dielectric layer on the substrate;forming a second dielectric layer on the first dielectric layer; formingthe plurality of conductive features of the first tier structure on thesecond dielectric layer; forming a middle dielectric layer on the seconddielectric layer and surrounding the plurality of conductive features ofthe first tier structure; forming the decoupling unit between theplurality of conductive features of the first tier structure; forming athird dielectric layer on the middle dielectric layer; and forming afourth dielectric layer on the third dielectric layer.
 17. The methodfor fabricating the semiconductor device of claim 16, wherein the firstdielectric layer and the third dielectric layer comprise the samematerial.